Abstract: With the application of a plasticity model for large post-liquefaction deformation of sand to model the liquefiable soil and an equivalent nonlinear incremental model to model stone columns (SC), three-dimensional dynamic responses of stone columns composite foundation in liquefiable soil are numerically investigated using finite difference code FLAC3D. The analysis investigates the effect of the SC’s high stiffness and improved drainage on soil liquefaction mitigation, the excess pore water pressure (EPWP) build-up and dissipation, the deformation process of the liquefiable soil from small to large deformation in the pre- and post-liquefaction regimes, and the variation of stress distribution between SC and surrounding soils. The results show that the model and the program can reasonably reproduce the seismic response of stone columns composite foundation in liquefiable soils and its effect of liquefaction mitigation. The vertical stress and horizontal shear stress gradually concentrate to SC during earthquake shaking and vertical effective stress ratio may decrease to 1/6-1/3, the deformation in soil and SC is incompatible and the ratio of shear strain in the soil and SC may reach 7-10. A ratio of SC permeability to soil permeability larger than 100 significantly decreases the EPWP, while the stiffness of SC slightly decreases EPWP but helps reduce the surface peak acceleration.

Key words: seismic response, liquefiable foundation, stone columns, liquefaction mitigation, FLAC3D